Skip to main content

Full text of "Text Book Of Mechanical Engineering"

See other formats

Appendix II.                              863

Total energy = Potential energy + Kinetic energy,     and


Total steam energy = (P x D) + w~

where w = weight of moving parts. Hence, as ordinates A M F B
shew total energy, and A L j B the load energy absorbed, the re-
maining ordinates, by deduction, viz., those of A M K L, will indicate
kinetic energy of moving parts. Now,

*2L = K.E.    /. v = V^y^-   X/K.KX4-I4
and V =  VK.E. x 24*8

where energy is in foot tons, and w = 6 tons.     Next, ordinates
K.E. are measured on A L K, and velocity curve found by calculation
The stroke will finish at P, directly under K, where v equals o ; and
the maximum velocity is at N, vertically over Q, where load and steam
curves cross.    Cut off occurs at •£% of stroke A P.

P. 492. Acceleration Curves.—It was shewn at p. 492 how
to construct an acceleration curve to a distance base. The proof
will here be given by reference to Fig. 825. Let V be a velocity
ordinate, whose growth v in a small portion of time / takes place
at A; also let a small distance d be traversed during time /.
x T is a tangent to the curve, and A B a normal; then D B or x
will shew the acceleration fy for


J     t      d    /

But - = velocity V,       for space = tv

and ^ = ™. by similar triangles.    Substituting

The construction cannot be reversed to find v, but \v^ may be
found by summation^ and V be therefrom deduced.

P. 496. Comparison of Angular Velocities in Link-

work. — In pp. 490-496 are found the linear velocities of points in
linkwork. But it is often convenient to know the ratios of
angular velocities in a pair of links, and two cases will here